The invention relates to the field of optical angle measurement apparatus.
Angle measurement apparatus are used, for example, as pure theodolites for measuring angles, or, combined for example with electro-optical distance measurement apparatus, as part of a coordinate measurement system. In a theodolite, the horizontal pivot typically has a V-bearing, i.e. a friction bearing with two defined contact points. The V-bearing however has the disadvantage that it may only be loaded in one direction, which prevents a non-perpendicular set-up, and renders the motoric drive more difficult on account of the changing drive force direction.
Other bearings with a low radial play are air bearings and stressed ball bearings. Apparatus such as laser trackers comprise stressed ball bearings. Whereas air bearings are awkward and large, the stressed ball bearings have the disadvantage that the balls no longer roll in an ideal manner, since they have to be stressed to a very great extent on account of the demand for a minimal radial deviation error. The influence of the temperature on the stressing, depending on the material selection, entails further complications.